Electrophotographic photoreceptor containing a bisstilbene compound

ABSTRACT

An electrophotographic photoreceptor is disclosed, comprising a conductive support having provided thereon a light-sensitive layer containing at least one of a specific type of bisstilbene compound as a photoconductive substance or a charge transporting material. The photoreceptor has high sensitivity, a small residual potential, and stability to ozone, light, or heat.

FIELD OF THE INVENTION

This invention relates to an electrophotographic photoreceptor, and,more particularly, to an electrophotographic photoreceptor having alayer containing a novel charge transporting material and to anelectrophotographic photoreceptor having a layer containing a novelphotoconductive substance.

BACKGROUND OF THE INVENTION

In electrophotographic photoreceptors, photoconduction takes placethrough (1) a process of generating electric charge upon exposure tolight and (2) a process of charge transport.

Electrophotographic photoreceptors wherein both the processes (1) and(2) are effected by the same substance include selenium photoreceptors,and those wherein the processes (1) and (2) are separately carried outby different substances include a combination of amorphous selenium andpoly-N-vinylcarbazole. The latter technique in which the processes (1)and (2) are effected by different substances advantageously allows awide choice in the kind of materials to be used for photoreceptors,which leads to improvement of electrophotographic characteristics, suchas sensitivity of photoreceptors, acceptable potential, etc. Further,such a large choice of materials means that materials favorable to theformation of photoreceptor coating films can be selected from a widerange.

Photoreceptors in electrophotography are essentially required to satisfythe following performance properties: (1) they can be charged at anappropriate potential in the dark; (2) dark decay of the charge issmall; (3) they are capable of rapidly discharging upon lightirradiation; and the like. The above-described inorganic substancescertainly have many merits but, at the same time, involve variousdemerits. For example, selenium, which is widely employed at this time,fully satisfies the above requirements (1) to (3), but involvesdifficult conditions of production, with the ultimate disadvantage ofincreased production cost. Further, it is difficult to shape selenium inthe form of a belt due to its lack of flexibility, and seleniumphotoreceptors need delicate handling due to high sensitivity to heatand mechanical shocks. Photoreceptors in which cadmium sulfide or zincoxide is dispersed in a resin binder have mechanical drawbacks in termsof surface smoothness, hardness, tensile strength, abrasion resistance,and the like, so that they cannot be used repeatedly.

In attempts to overcome these disadvantages of inorganic materials,electrophotographic photoreceptors using various organic materials haverecently been proposed, and some of them have been turned to practicaluse. For example, U.S. Pat. No. 3,484,237 discloses a photoreceptorcomprising poly-N-carbazole and 2,4,7-trinitrofluoren-9-one; JapanesePatent Publication No. 25658/73 discloses a photoreceptor comprisingpoly-N-vinylcarbazole sensitized with a pyrylium compound; and JapanesePatent Application (OPI) No. 10785/72 describes a photoreceptorcomprising mainly an eutectic complex composed of a dye and a resin (theterm "OPI" as used herein refers to a "published unexamined Japanesepatent application").

Another attempt has been directed to highly sensitiveelectrophotographic photoreceptors comprising a combination of amaterial capable of generating electric charge by light (called chargegenerating material) and a material capable of transporting thegenerated charge (called charge transporting material). Examples of suchphotoreceptors so far proposed include a photoreceptor having a chargegenerating layer having further provided thereon a charge transportinglayer as disclosed in U.S. Pat. No. 3,791,826; a photoreceptor having acharge transporting layer having further provided thereon a chargegenerating layer as disclosed in U.S. Pat. No. 3,573,906; and aphotoreceptor having a light-sensitive layer comprising a chargetransporting material having dispersed therein a charge generatingmaterial as taught in U.S. Pat. No. 3,764,315. With respect to this typeof photoreceptors, many useful charge generating materials have so farbeen proposed, but not so many as for truly useful chage transportingmaterials. Excellent charge transporting materials are those capable oftransmitting light of a wavelength causing a charge generating materialto generate charges through themselves to the charge generatingmaterial, maintaining a sufficient potential when charged, and rapidlytransporting the charges generated by the charge generating material.

SUMMARY OF THE INVENTION

An object of this invention is to provide an electrophotographicphotoreceptor having an electrophotographic light-sensitive layercontaining a charge transporting material permeable to light of awavelength causing charge generation.

Another object of this invention is to provide an electrophotographicphotoreceptor having an electrophotographic light-sensitive layershowing high sensitivity and a low residual potential.

Still another object of this invention is to provide anelectrophotographic photoreceptor having an electrophotographiclight-sensitive layer which is stable to oxidation by ozone generated bycorona charge, stable to light or heat, and in which dark decay of thepotential is reduced, the residual potential is not liable to increaseor vary due to repeated use, and sensitivity is not liable to vary.

A further object of this invention is to provide an electrophotographicphotoreceptor which can be handled and disposed of with safety, havingan electrophotographic light-sensitive layer containing a non-toxic orless toxic charge transporting material which can be synthesized fromnon-toxic or less toxic starting compounds.

A still further object of this invention is to provide a stable anduniform charge transporting layer having high film strength and highfatigue performance.

As a result of extensive investigations, the inventors have found thatbisstilbene compounds as hereinafter described effectively serve ascharge transporting materials in electrophotographic photoreceptors, andreached the present invention based on this finding.

The present invention relates to an electrophotographic photoreceptorhaving a light-sensitive layer containing at least one bisstilbenecompound represented by formula (I) ##STR1## wherein Ar represents asubstituted or unsubstituted aromatic carbon ring residue or asubstituted or unsubstituted aromatic heterocyclic residue; R¹ and R²(which may be the same or different) each represents a substituted orunsubstituted alkyl group, a substituted or unsubstituted aralkyl group,or a substituted or unsubstituted aryl group, or R¹ and R² together forman N-containing heterocyclic group; R³ represents a hydrogen atom, ahalogen atom, a substituted or unsubstituted alkyl group, a substitutedor unsubstituted alkoxy group, a substituted or unsubstituted arylgroup, a substituted or unsubstituted aralkyl group, or a substituted orunsubstituted aryloxy group; R⁴ represents a hydrogen atom, asubstituted or unsubstituted alkyl group, a substituted or unsubstitutedaralkyl group, or a substituted or unsubstituted aryl group; R⁵represents a hydrogen atom, a halogen atom, a nitro group, a cyanogroup, a substituted or unsubstituted alkyl group, a substituted orunsubstituted aralkyl group, or a substituted or unsubstituted arylgroup, or R⁵ together with Ar forms an aromatic ring; k represents 0 or1; and X represents a group represented by formula (II) ##STR2## whereinR⁷ and R⁸ each represents a hydrogen atom, a halogen atom, a substitutedor unsubstituted alkyl group, a substituted or unsubstituted alkoxygroup, a substituted or unsubstituted aryl group, or a substituted orunsubstituted aryloxy group, or R⁷ and R⁸ may be taken together to forma condensed polycyclic aromatic ring; l and n each represents 0 or aninteger of from 1 to 6; and m represents 0 or 1.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 4 each illustrates a corss-sectional view of theelectrophotographic photoreceptor according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The bisstilbene compounds represented by formula (I) can be used in anylight-sensitive layer according to the following embodiments (1) to (4):

(1) A single-layer light-sensitive layer containing both a chargegenerating material and the bisstilbene compound (I).

(2) A single-layer light-sensitive layer containing both a sensitizingdye and the bisstilbene compound (I).

(3) A laminated light-sensitive layer comprising a charge generatinglayer containing a charge generating material and a charge transportinglayer containing the bisstilbene compound (I).

(4) A laminated light-sensitive layer comprising a charge generatinglayer containing a charge generating material and the bisstilbenecompound (I) and a charge transporting layer containing a chargetransporting material.

The bisstilbene compounds of formula (I) according to the presentinvention will be described in more detail.

The unsubstituted alkyl group as represented by R¹, R², R³, R⁴, or R⁵includes a methyl group, an ethyl group, a propyl group, a butyl group,a pentyl group, a hexyl group, an octyl group, a nonyl group, a dodecylgroup, an isopropyl group, an isobutyl group, an isopentyl group, a4-methylpentyl group, a sec-butyl group, a t-butyl group, etc.

The unsubstituted aralkyl group as represented by R¹, R², R³, R⁴, or R⁵includes a benzyl group, a phenethyl group, a 1-naphthylmethyl group, a2-naphthylmethyl group, a 1-anthrylmethyl group, a benzhydryl group,etc.

The unsubstituted aryl group as represented by R¹, R², R³, R⁴, or R⁵includes a phenyl group, a 1-naphthyl group, a 2-naphthyl group, ananthryl group, a pyrenyl group, an acenaphthenyl group, a fluorenylgroup, etc.

The N-containing heterocyclic group jointly formed by R¹ and R² includesa piperazinyl group, etc.

The halogen atom as represented by R³ or R⁵ includes a chlorine atom, abromine atom, and an iodine atom.

The unsubstituted alkoxy group as represented by R³ includes a methoxygroup, an ethoxy group, a propoxy group, a butoxy group, a pentyloxygroup, etc. The unsubstituted aryloxy group as represented by R³includes a phenoxy group, an o-tolyloxy group, an m-tolyloxy group, ap-tolyloxy group, a 1-naphthyloxy group, a 2-naphthyloxy group, etc.

The unsubstituted aromatic carbon ring residue as represented by Arincludes a phenyl group, a naphthyl group, an anthryl group, a pyrenylgroup, an acenaphthenyl group, a fluorenyl group, etc. The unsubstitutedaromatic heterocyclic residue for Ar includes a pyridyl group, a thienylgroup, a carbazolyl group, etc.

The aromatic ring residue jointly formed by R⁵ and Ar includes a9-fluorenylidene group, etc.

The substituents for the substituted alkyl, aralkyl, or aryl group asrepresented by R¹, R², R³, R⁴, or R⁵ include a halogen atom, e.g., achlorine atom, a bromine atom, and an iodine atom; an alkoxy group,e.g., a methoxy group, an ethoxy group, a propoxy group, a butoxy group,a pentyloxy group; an aryloxy group, e.g., a phenoxy group, ano-tolyloxy group, an m-tolyloxy group, a p-tolyloxy group, a1-naphthyloxy group and a 2-naphthyloxy group; a dialkylamino group,e.g., a dimethylamino group, a diethylamino group, a dipropylaminogroup, an N-methyl-N-ethylamino group, an N-ethyl-N-propylamino group,and an N-methyl-N-propylamino group; a diarylamino group, e.g., adiphenylamino group; an alkylthio group, e.g., a methylthio group, anethylthio group, and a propylthio group; and an N-containingheterocyclic group, e.g., a piperidino group, a 1-piperazinyl group amorpholino group, and a 1-pyrrolidyl group.

In addition to the above-enumerated substituents, the substituents forthe substituted aryl group further include an alkyl group, e.g., amethyl group, an ethyl group, a propyl group, a butyl group, a pentylgroup, an isopropyl group, an isobutyl group, and an isopentyl group.

The substituents for the substituted aromatic carbon ring residue orsubstituted aromatic heterocyclic ring residue as represented by Arinclude those enumerated for the substituted aryl group.

Specific examples of the group represented by formula (II), i.e., X,include a methylene group, an ethylene group, a propylene group, abutylene group, a pentylene group, a hexylene group, a laurylene group,a p-xylylene group, a 2,5-dichloro-p-xylylene group, a2,3,5,6-tetramethyl-p-xylylene group, a 1,4-dimethylenenaphthalenegroup, etc.

R¹ and R² each preferably represents a methyl group, an ethyl group, ann-butyl group, an n-hexyl group, a benzyl group, and a phenyl group. R³preferably represents a hydrogen atom, a methyl group, an ethyl group, amethoxy group, an ethoxy group, a fluorine atom, a chlorine atom, and abromine atom. R⁴ preferably represents a hydrogen atom, a methyl group,an ethyl group, a phenyl group, a benzyl group, ap-(dimethylamino)phenyl group, and a p-(diethylamino)phenyl group, witha hydrogen atom being particularly preferred. R⁵ preferably represents ahydrogen atom or a phenyl group.

k preferably represents 0.

X preferably represents an ethylene group, a butylene group, a pentylenegroup, a hexylene group, and a p-xylylene group.

Specific but non-limiting examples of the bisstilbene compoundsrepresented by formula (I) according to the present invention are shownbelow. ##STR3##

The bisstilbene compounds of formula (I) can easily be obtained byreacting a compound represented by formula (III)

    Ar--CH.sub.2 Y                                             (III)

wherein Ar is as defined above; Y represents a triphenylphosphoniumgroup of the formula ##STR4## wherein Z.sup.⊖ represents a halogen ionor a dialkyl phosphite group of the formula --PO(OR')₂, wherein R'represents a lower alkyl group, with a compound represented by formula(IV) ##STR5## wherein X, R¹, R², R³, R⁴, and k are as defined above; inan organic solvent, e.g., dimethylformamide, etc., in the presence of anappropriate base, e.g., sodium hydride, sodium methoxide, potassiumt-butoxide, etc.

Of the starting compounds represented by formula (IV), those wherein R⁴is a hydrogen atom and k is 0, which correspond to the preferred amongthe compounds of formula (I), can be synthesized according to the methodof P. W. Hickmott, J. Chem. Soc., Vol. (C) (1966), p. 666.

The photoreceptors according to the present invention containing theabove-described bisstilbene compounds in accordance with the embodimentsas shown in FIGS. 1 to 4.

FIG. 1 shows a photoreceptor comprising a conductive support 1 havingprovided thereon light-sensitive layer 21 comprising the bisstilbenecompound, a sensitizing dye, and a binder (resin).

FIG. 2 shows a photoreceptor comprising a conductive support 1 havingprovided thereon light-sensitive layer 22 comprising charge transportingmedium 4 composed of the bisstilbene compound and a binder, whereincharge generating material 3 is dispersed in the medium 4.

FIG. 3 illustrates a photoreceptor comprising conductive support 1,having provided thereon light-sensitive layer 23 comprising a chargegenerating layer 5 consisting mainly of charge generating material 3 anda charge transporting layer containing the bisstilbene compound.

FIG. 4 illustrates a photoreceptor comprising conductive support 1having provided thereon light-sensitive layer 24 comprising chargetransporting layer 4 containing the bisstilbene compound and chargegenerating layer 5 consisting mainly of charge generating material 3.

In the photoreceptors shown in FIGS. 3 and 4, when a charge generatinglayer containing a charge generating material further contains thebisstilbene compound of the invention, the charge transporting layer maycontain charge transporting material other than the bisstilbenecompounds of the invention.

In the photoreceptors of FIG. 1, the bisstilbene compound acts as aphotoconductive substance, through which the formation and transport ofcharge carriers necessary for light decay are carried out. It should benoted, however, that in this embodiment the bisstilbene compound shouldbe sensitized with a sensitizing dye showing absorption in the visibleregion in order to form an image with visible light, because thebisstilbene compounds do not substantially absorb the visible region.

In the case of the photoreceptors of FIG. 2, the bisstilbene compoundcombined with a binder (or a binder and a plasticizer) forms a chargetransporting medium, while a charge generating material, such asinorganic or organic pigments, generates electric charge. In thisembodiment, the charge transporting medium principally functions toaccept and transport the charge generated by the charge generatingmaterial. Therefore, it is an essential condition that the chargegenerating material and the charge transporting compound should notoverlap each other in terms of absorption wavelength region, mostly inthe visible region. In other words, light should be transmitted to reachthe surface of the charge generating material in order to make thecharge generating material efficiently generate charge. To achieve thiseffect, the bisstilbene compound according to the present invention ischaracterized by having no substantial absorption in the visible regionso that when combined with a charge generating material generallyabsorbing light of the visible region, it effectively acts as a chargetransporting material.

In the photoreceptors of FIG. 3, the light transmitted through chargetransporting layer 4 reaches charge generating layer 5, wherein electriccharge is generated. On the other hand, the charge transporting layerserves to receive and transport the charge. The mechanism accounting forthe photoreceptors of FIG. 2, viz., that charge generation necessary forlight decay is achieved by a charge generating material and thattransport of charge is achieved by a charge transporting medium mainlycomprising the bisstilbene compound of the invention, is also applicableto the photoreceptors of FIG. 3.

In the photoreceptors of FIG. 4, charge generation takes place by theaction of light in charge generating layer 5, while charge transportinglayer 4 serves to receive and transport the charge. The same mechanismof charge generation and charge transport as described above is alsoapplicable to this embodiment, wherein the bisstilbene compound of theinvention works as a charge transporting material.

The photoreceptors of FIG. 1 can be prepared by coating a bindersolution having dissolved therein the bisstilbene compound, and, ifdesired, a sensitizing dye on a conductive support, followed by drying.The photoreceptors of FIG. 2 can be prepared by coating a conductivesupport with a solution of the bisstitlbene compound and a binder havingdispersed therein fine particles of a charge generating material,followed by drying.

For the production of the photoreceptors of FIG. 3, a charge generatinglayer is first formed by vacuum evaporation of a charge generatingmaterial onto a conductive support, or coating a dispersion of fineparticles of a charge generating material in an appropriate solvent, ifdesired, having dissolved therein a binder, drying the coating, and, ifnecessary, subjecting the coating to surface finishing, such as buffing,or controlling the film thickness. A charge transporting layer is thenformed thereon by coating a solution containing the bisstilbene compoundand a binder, followed by drying. The coating is carried out by aconventional means, such as a doctor blade, a wire bar, etc.

The photoreceptors of FIG. 4 can be produced by first forming a chargetransporting layer on a conductive layer in the same manner as for thephotoreceptors of FIG. 3 and then forming a charge generating layerthereon in the same manner as for the photoreceptors of FIG. 3.

The light-sensitive layer has a thickness of from 1 to 50 μm, andpreferably from 5 to 20 μm, in the photoreceptors of FIG. 1 or 2. In thephotoreceptors of FIGS. 3 and 4, the charge generating layer has athickness of not more than 5 μm, and preferably not more than 2 μm, andthe charge transporting layer has a thickness of from 3 to 50 μm, andpreferably from 5 to 20 μm.

In the photoreceptors of FIG. 1, the bisstilbene compound in thelight-sensitive layer is used in an amount of from 10 to 70% by weight,and preferably from 30 to 50% by weight, based on the light-sensitivelayer. The sensitizing dye which can be used for imparting sensitivityto the visible region is used in an amount of from 0.1 to 5% by weight,and preferably from 0.5 to 3% by weight, based on the light-sensitivelayer.

In the photoreceptors of FIG. 2, the bisstilbene compound in thelight-sensitive layer is used in an amount of from 10 to 95% by weight,and preferably from 30 to 90% by weight, based on the light-sensitivelayer, and the charge generating material is used in an amount of notmore than 50% by weight, and preferably not more than 20% by weight,based on the light-sensitive layer. In the photoreceptors of FIGS. 3 and4, the bisstilbene compound in the charge transporting layer is presentin an amount of from 10 to 95% by weight, and preferably from 30 to 90%by weight, based on the charge transporting layer. The charge generatingmaterial in the charge generating layer is present in an amount of from10 to 90% by weight, and preferably from 20 to 70% by weight, based onthe charge generating layer in cases when the charge generating layerdoes not contain the bisstilbene compound; and is present in an amountof from 0.01 to 90% by weight, and preferably from 0.05 to 70% byweight, based on the charge generating layer in cases when the chargegenerating layer contains the bisstilbene compound, with the bisstilbenecompound being present in an amount of from 0.01 to 70% by weight, andpreferably from 0.05 to 50% by weight, based on the charge generatinglayer. In each of the photoreceptors of FIGS. 1 to 4, the binder may beused in combination with a plasticizer.

The conductive support which can be used in the photoreceptors of theinvention includes metal plates or foils, such as an aluminum plate orfoil, plastic films on which a metal, e.g., aluminum, isvacuum-deposited, paper having a conductive coating, and the like.Binders to be used may be any of insulating and adhesive resins, such ascondensed resins, e.g., polyamide, polyurethane, polyester, epoxyresins, polyketone, polycarbonate, etc., and vinyl polymers, e.g.,polyvinylketone, polystyrene, poly-N-vinylcarbazole, polyacrylamide,etc.

Plasticizers to be used include halogenated paraffins, polybiphenylchloride, dimethylnaphthalene, dibutyl phthalate, etc.

The sensitizing dyes which can be used in the photoreceptors of FIG. 1include triallylmethane dyes, such as Brilliant Green, Victoria Blue B,Methyl Violet, Crystal Violet, Acid Violet 6B, etc.; xanthene dyes, suchas Rhodamine B, Rhodamine 6G, Rhodamine G Extra, Eosine S, Erythrocin,Rose Bengale, Fluorescein, etc.; thiazine dyes, such as Methylene Blue,etc.; Astrazone dyes, such as C.I. Basic Violet 7 (CI 48020); cyaninedyes, such as cyanine; pyrylium dyes, such as2,6-diphenyl-4-(N,N-dimethylaminophenyl)thiapyrylium perchlorate,benzopyrylium salts (disclosed in Japanese Patent Publication No.25658/83), etc.; and the like.

Examples of the charge generating materials which can be used in thephotoreceptors shown in FIGS. 2, 3, and 4 are listed below:

(1) selenium and selenium alloys;

(2) inorganic photoconductive materials, e.g., CdS, CdSe, CdSSe, ZnO,ZnS, etc.;

(3) phthalocyanine pigments, e.g., metal-phthalocyanine and metal-freephthalocyanine, etc.;

(4) azo pigments, such as azo pigments having a carbazole skeleton asdescribed in Japanese patent application (OPI) No. 95033/75, azopigments having a triphenylamine skeleton as described in Japanesepatent application (OPI) No. 132547/75, azo pigments having astyrylstilbene skeleton as described in Japanese patent application(OPI) Nos. 133445/75 and 42352/84, azo pigments having a naphthaleneskeleton as described in Japanese patent application (OPI) Nos.123541/83 and 217556/83, trisazo pigments as described in Japanesepatent application (OPI) No. 179746/85, azo pigments having a thiopheneskeleton as described in Japanese patent application (OPI) No.223433/84, etc.;

(5) perylene pigments, such as perylenic anhydride, perylenic acidimide, etc.;

(6) indigoid dyes;

(7) quinacridone dyes;

(8) polycyclic quinones; such as anthraquinones, pyrenequinones,anthanthrones, flavanthrones, etc.;

(9) bisbenzimidazole pigments;

(10) cyanine dyes;

(11) squaric methine dyes;

(12) indanthrone pigments;

(13) xanthene dyes;

(14) charge transporting complexes comprising an electron donor, e.g.,poly-N-vinylcarbazole, etc., and an electron acceptor, e.g.,trinitrofluorenone, etc.;

(15) eutectic complexes formed by pyrylium salt dyes and polycarbonateresins; and

(16) amorphous silicon.

Among these charge generating materials azo dyes are preferred.

Charge transporting materials other than the bisstilbene compounds ofthe present invention which can be used in the charge transporting layerare classified into electron transporting compounds and positive holetransporting compounds, and both of which can be used in theelectrophotographic photoreceptors of the present invention. Examples ofthe electron transporting compounds include compounds having an electronattractive group, such as 2,4,7-trinitro-9-fluorenone,2,4,5,7-tetranitro-9-fluorenone,9-dicyanomethylene-2,4,7-trinitrofluorenone,9-dicyanomethylene-2,4,5,7-tetranitrofluorenone,tetranitrocarbazolechloranil, 2,3-dichloro-5,6-dicyanobenzoquinone,2,4,7-trinitro-9,10-phenanthrenequinone, tetrachlorophthalic anhydride,tetracyanoethylene, tetracyanoquinonedimethane, etc.

The positive hole transporting compounds are compounds having anelectron donative group including high molecular weight compounds, suchas pyridonylcarbazole and its derivative as disclosed in Japanese PatentPublication No. 10966/59; vinyl polymers, e.g., polyvinylpyrene,polyvinylanthracene,poly-2-vinyl-4-(4'-dimethylaminophenyl)-5-phenyl-oxazole,poly-3-vinyl-N-carbazole, etc., as disclosed in Japanese PatentPublication Nos. 18674/68 and 19192/68; polymers described in JapanesePatent Publication No. 19193/68, e.g., polyacenaphthylene, polyindene, acopolymer of acenaphthylene and styrene, etc.; condensed resins, e.g.,pyrene-formaldehyde resins, bromopyrene-formaldehyde resins,ethylcarbazole-formaldehyde resins, etc., as disclosed in JapanesePatent Publication No. 13940/81; and various kinds of triphenylmethanepolymers as disclosed in Japanese patent application (OPI) Nos. 90833/81and 161550/81; and low molecular weight compounds, such as triazolederivatives as described in U.S. Pat. No. 3,112,197; oxadiazolederivatives as described in U.S. Pat. No. 3,189,447; imidazolederivatives as described in Japanese Patent Publication No. 16096/62;polyarylalkane derivatives as disclosed in U.S. Pat. Nos. 3,615,402,3,820,989, and 3,542,544, Japanese Patent Publication Nos. 555/70 and10983/72, and Japanese patent application (OPI) Nos. 93224/76, 17105/80,4148/81, 108667/80, 156953/80, and 36656/81; pyrazoline derivatives andpyrazolone derivatives as disclosed in U.S. Pat. Nos. 3,180,729 and4,278,746 and Japanese patent application (OPI) Nos. 88064/80, 88065/80,105537/74, 51086/80, 80051/81, 88141/81, 45545/82, 112637/79, and74546/80; phenylenediamine derivatives as disclosed in U.S. Pat. No.3,615,404, Japanese Patent Publication No. 10105/76, Japanese patentapplication (OPI) Nos. 83435/79, 110836/79, and 119925/79, and JapanesePatent Publication Nos. 3712/71 and 28336/72; arylamine derivatives asdisclosed in U.S. Pat. No. 3,567,450, Japanese patent publication No.35702/74, West German Patent (DAS) No. 1110518, U.S. Pat. Nos.3,180,703, 3,240,597, 3,658,520, 4,232,103, 4,175,961, and 4,012,376,Japanese patent application (OPI) Nos. 144250/80 and 119132/81, JapanesePatent Publication No. 27577/64 and Japanese patent application (OPI)No. 22437/81; amino-substituted chalcone derivatives as disclosed inU.S. Pat. No. 3,526,501; N,N-bicarbazyl derivatives as disclosed in U.S.Pat. No. 3,542,546; oxazole derivatives as disclosed in U.S. Pat. No.3,257,203; styrylanthracene derivatives as disclosed in Japanese patentapplication (OPI) No. 46234/81; fluorenone derivatives as disclosed inJapanese patent application (OPI) No. 110837/79; and hydrazonederivatives as disclosed in U.S. Pat. Nos. 3,717,462 and 4,150,987, andJapanese patent application (OPI) Nos. 52063/80, 52064/80, 46760/80,85495/80, 11350/82, and 148749/82.

If desired, the photoreceptors of the present invention may have anadhesive layer or a barrier layer between the conductive support and thelight-sensitive layer. Materials to be used in these auxiliary layersinclude gelatin, casein, polyvinyl alcohol, ethyl cellulose,carboxymethyl cellulose, vinylidene chloride latices as described inJapanese patent application (OPI) No. 84247/84, styrene-butadienelatices as described in Japanese patent application (OPI) No. 114544/84,etc., as well as the above-described high molecular weight polymersuseful as binders. These layers preferably have a thickness of not morethan 1 μm.

The electrophotographic photoreceptors in accordance with the presentinvention are, in general, characterized by high sensitivity andexcellent durability.

The electrophotographic photoreceptors of the present invention can beapplied widely to electrophotographic copying machines and printersusing a laser beam or a Braun tube as a light source. In addition, theycan also be used for the production of printing plates having highresolving power, high durability, and high sensitivity, in which thebisstilbene compound of the invention and a charge generating materialare dispersed in an alkali-soluble resin, e.g., a phenol resin, and thedispersion is coated on a conductive support, e.g., an aluminum sheet,dried, imagewise exposed to light, developed with a toner and thenetched with an alkali aqueous solution, as described, e.g., in Japanesepatent publication No. 17162/62 and Japanese patent application (OPI)Nos. 19063/80, 161250/80, and 147656/82. Likewise, printed circuits canbe produced by using the photoreceptors of the invention.

This invention will now be illustrated in greater detail with referenceto the following examples, but it should be understood that they are notintended to limit the present invention. In these examples, all theparts are given by weight.

SYNTHESIS EXAMPLE Synthesis of Compound (2)

In 30 ml of N,N-dimethylformamide were dissolved 4.85 g (0.02 mol) ofdiethyl 4-methylbenzylphosphonate and 3.80 g (0.01 mol) ofbis(N-n-butyl-4-formulanilino)butane, and 5.79 g of sodium methoxide (28wt% methanolic solution) was added to the solution at 20° C. Theresulting mixture was heated at 60° C. for 10 hours, followed by coolingto room temperature, and 30 ml of ethanol was added thereto. The formedcrystals were collected by filtration, washed with water andrecrystallized from a mixed solvent of ethyl acetateethanol to give 4.36g (yield: 78%) of Compound (2) as yellow needle-like crystals.

Melting Point: 169°-170° C.

Elementary Analysis for C₄₀ H₄₈ N₂ : Calcd. (%): C 86.28, H 8.69, N5.03, Found (%): C 86.48, H 8.73, N 4.79.

EXAMPLE 1

Selenium was vacuum-evaporated onto an about 300 μm thick grainedaluminum sheet to form a charge generating layer having a thickess of0.4 μm. A solution of 10 parts of Compound (2) and 10 parts of bisphenolA polycarbonate (Panlite K-1300; produced by Teijin Limited) in 130parts of dichloromethane was coated on the charge generating layer usinga wire round rod, followed by drying to form a charge transporting layerhaving a thickness of about 12 μm. There was obtained anelectrophotographic photoreceptor having a light-sensitive layercomposed of two layers.

The resulting photoreceptor was negatively charged by corona dischargeof -5 KV by the use of an electrostatic copying paper testing equipment(SP-428, manufactured by Kawaguchi Denki Seisakusho) and then irradiatedwith light emitted from a tungsten lamp of 2,854° K. at an illuminanceof 2.0 lux. The half-decay, i.e., the time required for the surfacepotential to be reduced to one-half its initial value, was determined toobtain a half-decay exposure amount (E₅₀ : lux.sec). As a result, thehalf-decay exposure amount was 1.8 lux.sec.

After the above-described charging and light exposure were repeated3,000 times, E₅₀ was 2.0 lux.sec, indicating an extremely smallfluctuation in sensitivity.

EXAMPLES 2 TO 6

A photoreceptor was produced in the same manner as described in Example1, except using Compounds (1), (7), (10), (16) and (26), respectively,in place of Compound (2). A half-decay exposure amount (E₅₀) whennegatively charged was determined, and the results obtained are shown inTable 1 below.

                  TABLE 1                                                         ______________________________________                                        Example      Bisstilbene E.sub.50                                             No.          Compound (I)                                                                              (lux · sec)                                 ______________________________________                                        2             (1)        2.2                                                  3             (7)        3.0                                                  4            (10)        2.3                                                  5            (16)        1.9                                                  6            (26)        3.3                                                  ______________________________________                                    

EXAMPLE 7

Five parts of beta-copper phthalocyanine were added to 660 parts ofdichloromethane, followed by ultrasonic dispersion. In the dispersionwere dissolved 40 parts of bisphenol A polycarbonate (Panlite K-1300)and 40 parts of Compound (2) to prepare a coating composition. Thecoating composition was coated on a transparent conductive supportcomprising a 100 μm thick polyethylene terephthalate sheet havingprovided thereon an indium oxide deposited film (surface resistivity:10³ Ω) using a wire round rod and dried to obtain a photoreceptor havinga thickness of about 10 μm.

The half-decay exposure amount (E₅₀) of the resulting photoreceptor whenpositively charged by corona discharge of +5 KV was 3.5 lux·sec.

EXAMPLE 8

Two parts of a trisazo pigment of the following formula and 4 parts of apolyester resin (Vylon 200, manufactured by Toyo Spinning Co., Ltd.)were added to 7 parts of tetrahydrofuran, and the mixture was dispersedin a ball mill for 12 hours. The resulting dispersion was coated on aconductive support comprising a 100 μm thick polyethylene terephthalatesheet having an aluminum deposited film; (surface resistivity: 4×10² Ω)using a wire round rod, followed by drying to form a charge generatinglayer having a thickness of about 0.5 μm.

A solution of 10 parts of Compound (2) and 10 parts of bisphenol Apolycarbonate (Panlite K-1300) in 120 parts of dichloromethane wascoated on the charge generating layer with a wire wound rod and dried toform a charge transporting layer having a thickness of about 14 μm.

A half-decay exposure amount (E₅₀) of the resulting photoreceptor asdetermined in the same manner as in Example 1 was 1.6 lux·sec.

Trisazo Pigment: ##STR6##

EXAMPLES 9 TO 20

A photoreceptor having a two-layer structure was prepared in the samemanner as described in Example 8, except replacing Compound (2) withCompound (4), (5), (9), (11), (13), (18), (19), (21), (24), (25), (30),or (32). A half-decay exposure amount (E₅₀) was determined in the samemanner as in Example 1, and the results obtained are shown in Table 2below.

                  TABLE 2                                                         ______________________________________                                        Example      Bisstilbene E.sub.50                                             No.          Compound (I)                                                                              (lux · sec)                                 ______________________________________                                         9            (4)        1.6                                                  10            (5)        1.9                                                  11            (9)        1.5                                                  12           (11)        1.7                                                  13           (13)        2.3                                                  14           (18)        1.7                                                  15           (19)        1.3                                                  16           (21)        1.5                                                  17           (24)        1.9                                                  18           (25)        2.4                                                  19           (30)        2.1                                                  20           (32)        3.0                                                  ______________________________________                                    

EXAMPLE 21

Eight parts of Compound (2), 10 parts of bisphenol A polycarbonate(panlite K-1300) and 0.12 part of an astrazon dye of the followingformula were dissolved in 100 parts of dichloromethane to prepare acoating composition. The coating composition was coated on a transparentconductive support comprising a 100 μm thick polyethylene terephthalatesheet having an indium oxide deposited film (surface resistivity: 10³ Ω)with a wire round rod and dried to obtain a photoreceptor having athickness of about 10 μm.

The resulting photoreceptor was positively charged by corona dischargeof +5 KV, and a half-decay exposure amount (E₅₀) was found to be 13.2lux·sec.

Astrazon Dye: ##STR7##

EXAMPLE 22

Five parts of the same trisazo pigment as used in Example 8, 40 parts ofCompound (2) and 100 parts of a benzyl methacrylate-methacrylic acidcopolymer (methacrylic acid content: 32.9%; [η]=0.12 in methyl ethylketone at 30° C.) were dispersed in 660 parts of dichloromethane byultrasonic wave. The resulting dispersion was coated on a grainedaluminum plate having a thickness of 0.25 mm and dried to obtain anelectrophotographic printing plate precursor. The precursor was chargedby corona discharge (+6 KV) in the dark so as to have a surfacepotential of +600 V and then exposed to light emitted from a tungstenlamp (color temperature: 2,854° K.) at an illuminance of 2.0 lux. Ahalf-decay exposure amount (E₅₀) was 2.0 lux·sec.

The printing plate precursor was charged in the dark so as to have asurface potential of about +400 V and imagewise exposed to light througha transparent positive original in intimate contact therewith. Theexposed plate was dipped in a developing solution comprising 5 g ofpolymethyl methacrylate (toner) finely dispersed in 1 liter of apetroleum solvent (Isopar H, produced by Esso Standard Co,, Ltd.) and0.01 g of soybean lecithin thereby to form a clear positive toner image.The plate was heated at 100° C. for 30 seconds to fix the toner image.The printing plate precursor was then dipped in a solution consisting of70 g of sodium metasilicate hydrate, 140 ml of glycerin, 550 ml ofethylene glycol and 150 ml of ethanol for about 1 minute, followed bywashing with running water while lightly brushing to remove thelight-sensitive layer in the areas where no toner was attached, tothereby obtain a printing plate.

Instead of using the above-described developing solution, theelectrostatic latent image was subjected to magnetic brush developmentusing a toner for Xerox 3500 (produced by Fuji Xerox Co., Ltd.),followed by heating at 80° C. for 30 seconds to fix the toner image. Thelight-sensitive layer in the areas where no toner was attached wasremoved with an alkali solution to obtain a printing plate.

When the thus-produced printing plate was mounted on an offset printer(Hamadastar 600CD) and printing was carried out, 50,000 prints that werevery clear with no background stain could be obtained.

EXAMPLE 23

A solution of 3 parts of Compound (2) and 5 parts of a polyester resin(Vylon 200, produced by Toyo Spinning Co., Ltd.) in 44 parts oftetrahydrofuran and 5 g of a disazo pigment of the following formulawere dispersed in a ball mill for 20 hours. The resulting dispersion wascoated on a conductive support comprising a 75 μm thick polyethyleneterephthalate film having an aluminum deposited film (surfaceresistivity: 10³ Ω) with a wire round rod and dried to form a chargegenerating layer having a thickess of 0.6 μm.

Disazo Pigment: ##STR8##

A solution consisting of 2.4 parts of a hydrazone compound of thefollowing formula as a charge transporting material, 4 parts ofbisphenol A polycarbonate, 13,3 parts of dichloromethane 26.6 parts of1,2-dichloroethane was coated on the charge generating layer and driedto form a charge transporting layer having a thickness of 11 μm. Theresulting electrophotographic photoreceptor having a two-layeredlight-sensitive layer was designated as Sample A.

Hydrazone Compound: ##STR9##

For comparison, Sample B was produced in the same manner as describedabove except that Compound (2) was not used.

Each of Samples A and B was charged by corona discharge of -6 KV for 5seconds by means of an electrostatic copying paper testing equipment(SP-428, produced by Kawaguchi Denki K.K.) and allowed to stand for 10seconds in a dark place. Then, the potential of the sample wasdetermined and referred to as initial surface potential V₀. Then, thesample was irradiated with light emitted from a tungsten lamp (colortemperature: 2,854° K.) at an illuminance of 2 lux to determine ahalf-decay exposure amount (E₅₀). The results obtained are as follows:

Sample A, E₅₀ =2.1 lux·sec,

Sample B, E₅₀ =3.4 lux·sec.

The above measurement was repeated 200 times, and the results obtainedare shown in Table 3.

                  TABLE 3                                                         ______________________________________                                                              Potential (V.sub.0) after                                          Initial    Repeated Use of                                                    Potential (V.sub.0)                                                                      200 Times                                               Sample     (V)        (V)                                                     ______________________________________                                        A          -554       -535                                                    B          -511       -150                                                    ______________________________________                                    

It can be seen from the results of Table 3 that Sample A wherein thebisstilbene compound of the invention is added to the charge generatinglayer is superior in sensitivity to Sample B containing no bisstilbenecompound and that the reduction in initial surface potential due torepeated charging processing is much smaller in Sample A than in SampleB.

EXAMPLES 24 TO 29

An electrophotographic photoreceptor was produced in the same manner asin Example 23 but replacing Compound (2) with Compound (1), (3), (5),(6), (12), or (31).

Then, the resulting photoreceptor was tested for the half-decay exposureamount (E₅₀), the initial surface potential (V₀) and the initial surfacepotential after repeated use of 200 times in the same manner asdescribed in Example 23. The results obtained are shown in Table 4.

                  TABLE 4                                                         ______________________________________                                                       V.sub.0                                                                             Initial  Potential after                                 Example  E.sub.50    Potential                                                                              200 Times                                       No.      (lux · sec)                                                                      (V)      (V)                                             ______________________________________                                        24       2.8         -602     -587                                            25       2.4         -648     -562                                            26       2.4         -702     -691                                            27       2.9         -728     -698                                            28       2.5         -648     -549                                            29       2.1         -656     -539                                            ______________________________________                                    

As can be seen from the above results, photoreceptors wherein thebisstilbene compounds are added to the charge generating layer havehigher sensitivity and reduction in charged potential due to repeatedcharging processing is much smaller as compared with Sample B of Example23.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:
 1. An electrophotographic photoreceptor comprising aconductive support having provided thereon a light-sensitive layer,wherein said light-sensitive layer contains at least one bisstilbene orbisstyryl compound represented by formula (I) ##STR10## wherein Arrepresents a substituted or unsubstituted atomatic carbon ring residueor a substituted or unsubstituted aromatic heterocyclic residue; R¹ andR² each represents a substituted or unsubstituted alkyl group, asubstituted or unsubstituted aralkyl group, or a substituted orunsubstituted aryl group, or R¹ and R² together form an N-containingheterocyclic group; R³ represents a hydrogen atom, a halogen atom, asubstituted or unsubstituted alkyl group, a substituted or unsubstitutedalkoxy group, a substituted or unsubstituted aryl group, a substitutedor unsubstituted aralkyl group, or a substituted or unsubstitutedaryloxy group; R⁴ represents a hydrogen atom, a substituted orunsubstituted alkyl group, a substituted or unsubstituted aralkyl group,or a substituted or unsubstituted aryl group; R⁵ represents a hydrogenatom, a halogen atom, a nitro group, a cyano group, a substituted orunsubstituted alkyl group, a substituted or unsubstituted aralkyl group,or a substituted or unsubstituted aryl group, or R⁵ together with Arforms an aromatic ring; k represents 0 or 1; and x represents a grouprepresented by formula (II) ##STR11## wherein R⁷ and R⁸ each representsa hydrogen atom, a halogen atom, a substituted or unsubstituted alkylgroup, a substituted or unsubstituted alkoxy group, a substituted orunsubstituted aryl group, or a substituted or unsubstituted aryloxygroup, or R⁷ and R⁸ together form a condensed polycyclic aromatic ring;l and n each represents 0 or an integer of from 1 to 6; and m represents0 or
 1. 2. An electrophotographic photoreceptor as in claim 1, whereinR¹ and R² each represents a methyl group, an ethyl group, an n-butylgroup, an n-hexyl group, a benzyl group, or a phenyl group.
 3. Anelectrophotographic photoreceptor as in claim 1, wherein R³ represents ahydrogen atom, a methyl group, an ethyl group, a methoxy group, anethoxy group, a fluorine atom, a chlorine atom, or a bromine atom.
 4. Anelectrophotographic photoreceptor as in claim 1, wherein R⁴ represents ahydrogen atom, a methyl group, an ethyl group, a phenyl group, a benzylgroup, a p-(dimethylamino)phenyl group, or a p-(diethylamino)phenylgroup.
 5. An electrophotographic photoreceptor as in claim 1, wherein R⁵represents a hydrogen atom, or a phenyl group.
 6. An electrophotographicphotoreceptor as in claim 1, wherein k is
 0. 7. An electrophotographicphotoreceptor as in claim 1, wherein X represents an ethylene group, abutylene group, a pentylene group, a hexylene group, or a p-xylenegroup.
 8. An electrophotographic photoreceptor as in claim 1, whereinsaid light-sensitive layer is composed of a charge generating layerhaving a thickness of not more than 5 μm containing a charge generatingmaterial and a charge transporting layer containing said compound offormula (I).
 9. An electrophotographic photoreceptor as in claim 8,wherein said charge generating layer further contains said compound offormula (I).
 10. An electrophotographic photoreceptor as in claim 8,wherein R¹ and R² each represents a methyl group, an ethyl group, ann-butyl group, an n-hexyl group, a benzyl group, or a phenyl group, R³represents a hydrogen atom, a methyl group, an ethyl group, a methoxygroup, an ethoxy group, a fluorine atom, a chlorine atom, or a bromineatom, R⁴ represents a hydrogen atom, a methyl group, an ethyl group, aphenyl group, a benzyl group, a p-(dimethylamino)phenyl group, or ap-(diethylamino)phenyl group, R⁵ represents a hydrogen atom, or a phenylgroup, k is 0, and X represents an ethylene group, a butylene group, apentylene group, a hexylene group, or a p-xylene group.
 11. Anelectrophotographic photoreceptor as in claim 1, wherein saidlight-sensitive layer contains at least one bisstilbene or bisstyrylcompound represented by formula (I) and a binder, said bisstilbene orbisstyryl compound being present in an amount of from 10 to 70% byweight based on the light-sensitive layer.
 12. An electrophotographicphotoreceptor as in claim 11, wherein said light-sensitive layer furthercontains a sensitive dye in an amount of from 0.1 to 5% by weight basedon the light-sensitive layer.
 13. An electrophotographic photoreceptoras in claim 1, wherein said light-sensitive layer contains at least onebisstilbene or bisstyryl compound represented by formula (I), a chargegenerating material in an amount of not more than 50% by weight and abinder, said bisstilbene or bisstyryl compound being present in anamount of from 10 to 95% by weight based on the light-sensitive layer.14. An electrophotographic photoreceptor as in claim 8, wherein saidcharge transporting layer contains a bisstilbene or bisstyryl compoundrepresented by formula (I) in an amount of from 10 to 95% by weightbased on the charge transporting layer.
 15. An electrophotographicphotoreceptor as in claim 9, wherein said charge generating layercontains a bisstilbene or bisstyryl compound represented by formula (I)in an amount of from 0.01 to 70% by weight and a charge generatingmaterial in an amount of from 0.01 to 90% by weight, based on the chargegenerating layer.
 16. An electrophotographic photoreceptor as in claim1, wherein said light-sensitive layer is composed of a charge generatinglayer containing a bisstilbene or bisstyryl compound represented byformula (I), and a charge transporting layer containing a chargetransporting material.
 17. An electrophotographic photoreceptor as inclaim 16, wherein said charge generating layer contains a bisstilbene orbisstyryl compound represented by formula (I) in an amount of from 0.01to 70% by weight and a charge generating material in an amount of from0.01 to 90% by weight, based on the charge generating layer.